First, a will comes into play AFTER a person dies. So, as long as your father has not changed his will (and he must be competent to do so), the division of the property among the siblings will remain as it is written in the will. However, if the will is, or has been changed, due to the undue influence of your brother over your father, or because your brother wants more of the estate, you and your other sibling may institute a "will contest" in probate court after your father passes.
A Power of Attorney is in effect while the person is alive. If your brother is the "attorney in fact" for your father regarding health care decisions, then that means that your brother may make those decision for your father ONLY IF your father can not make those decisions for himself.
If your brother is "attorney in fact" over your father's finances, that means that your brother can make decisions regarding your father's bank accounts, stocks, bonds, real estate, etc. However, a Power of Attorney may also be limited in the powers that it gives the "attorney in fact."
When a person wants to make legal decisions for another as to the placement, living arrangements, etc. of the person, USUALLY, a person (your brother) would have to go to the Probate Court and Petition the Court for Guardianship
over the person of your father. The reason for such a guardianship would be that your father cannot make decisions on his own behalf, and that he is "incompetent" to do so. The incompetency can be physical and/or mental. For example, if your father has Alzheimer's and can no longer make decisions on his own, a Petition for Guardianship would have to be brought before the Court. The Petition can be brought by anyone or even an agency. If your brother filed a Petition for Guardianship over the person of your father, you and/or your other sibling could object to the Guardianship.
It is important to remember that the provisions of a Will ONLY come into play after the death of the Testator (your father). Guardianships, conservatorships, or powers of attorney are in play while your father is alive.
You need to request to see a copy of the Power of Attorney(s) that your father has in his possession, or that he has signed and given to your brother. The Power of Attorney will spell out, in detail, the powers granted to the attorney in fact (your brother).
I hope you find this information useful.
My goal is to provide you with excellent service – if you feel you have gotten anything less, please reply back. I am happy to address follow-up questions. If you are satisfied with my answer, please rate it as "excellent" or in another positive manner. That is the only way that I can get credit for answering the question.
Thank you for your business!